With the reduction in size and weight of electronic and electric devices, there is an increasing demand for reductions in size and weight of secondary batteries. However, currently available secondary batteries have a complicated internal structure, so that there is a limit to improvements in electrical capacity per a given volume of a device. Also, complicated structure prevents improvements in reliability of batteries in some aspects. For example, a current-collecting tab or a current-collecting lead connected to an electrode may interfere with a homogeneous electrode reaction in the plane of the electrode. In the event that a cut section of the lead has metallic burrs that are larger than usual, an internal short-circuit may occur.
Secondary batteries have an electrode plate assembly including a positive electrode, a negative electrode and a separator. The electrode plate assembly is either of a layered type or a wound type. A layered type electrode plate assembly is obtained by alternately layering positive electrodes and negative electrodes with separators interposed between them. Also, a wound type electrode plate assembly is obtained by winding a long positive electrode and a long negative electrode with a separator between them. Such an electrode plate assembly usually has side faces where the edges of the positive and negative electrodes are flush with one another. In order to take out electricity from such side faces without causing an internal short-circuit, current-collecting tabs or current-collecting leads are necessary.
From the viewpoint of simplifying the internal structure of batteries, it has been proposed to cause a positive electrode to protrude from one side face of an electrode plate assembly and cause a negative electrode to protrude from the side face opposite the above-mentioned side face, in order to directly take out electricity from each side face without using current-collecting tabs or current-collecting leads. For example, for batteries with a layered type electrode plate assembly, a technique of integrally joining protruded electrode plates of the same polarity with a predetermined metal member has been proposed in Japanese Laid-Open Patent Publication No. 2001-126707. Also, for batteries with a wound type electrode plate assembly, a technique of joining the core material of a protruded electrode plate of the same polarity with a plate-shaped current collector plate has been proposed in Japanese Laid-Open Patent Publication No. 2000-294222.
However, in such cases where the positive electrode is caused to protrude from one side face of the electrode plate assembly and the negative electrode is caused to protrude from the side face opposite the above-mentioned side face, electrode plate assemblies must be produced one by one, so that the manufacturing process of the electrode plate assembly becomes complicated. That is, a problem of being unable to manufacture a plurality of electrode plate assemblies at the same time arises.
Also, it is known that when batteries are being charged/discharged, Joule's heat is generated in the batteries. In this case, as more current flows during charging/discharging, more heat is generated and more damage is caused by heat to battery components, which poses a problem. Also, there is another problem particularly with high-output batteries such as lithium batteries. When they become short-circuited, a large current flows, thereby resulting in a considerable increase in battery temperature.
In view of the above, an object of the present invention is to provide an electrochemical device with a simple structure, a high thermal reliability and a high electrical capacity. Also, another object is to provide electrochemical devices that can be efficiently manufactured in a large number at the same time.